The present invention generally relates to optical fiber configurations and fabrication methods, and more specifically to multimode optical fiber configurations and fabrication methods.
Bend-resistant multimode fibers (MMFs) often possess a graded-index core region and a cladding region, both regions comprising silica. The cladding region can include multiple cladding segments with some segments containing up-dopant(s) and/or down-dopant(s). For example, the cladding region may include three annular segments—e.g., an inner annular segment, a down-doped, depressed-index segment and an outer annular segment. The cladding region can also include two annular segments—e.g., a depressed-index segment and an outer annular segment.
Conventional methods to fabricate the segments in the cladding region of these bend-resistant MMFs rely on silica deposition and doping steps limited to the creation of some, but not all of the segments in a given cladding region in one processing sequence. For example, an MMF having a cladding with three annular segments often will require multiple cladding deposition steps to complete the fiber. One set of processing conditions, including a silica deposition step, can be used to fabricate an inner annular segment and a depressed-index annular segment in the MMF. Another set of processing conditions, including a separate, second silica deposition step, can then be used to create the outer annular segment of the MMF. As such, fabricating bend-resistant MMFs is often a time-intensive and costly process that relies on a large number of processing steps and fiber manufacturing equipment.
Fabrication of bend-resistant MMF is also often limited by the techniques for down-doping the cladding region. It is known that extending a graded core refractive index profile into the portions of the cladding region immediately adjacent to the core can improve the peak bandwidth and bend insensitivity of the MMF. However, conventional MMF manufacturing methods and processes are not able to vary the concentration profile of down-dopants within a particular as-formed cladding segment (or segments).